This invention relates to radar antijamming devices, and more particularly to a multiple side-lobe canceller.
Side-lobe cancellation is a fundamental approach to elimination of jamming from received signals and uses jammer location to eliminate jamming signals and in effect maintains a null in the radar antenna receiver pattern in the direction of the jammer which is accomplished by using an omnidirectional antenna or antennas adjacent to the main radar antenna.
This invention is an improvement over that used in the past and avoids the problem of spurious beat signals that restrict bandwidth and performance. For example, in the output of a conventional canceller having a bandwidth of 4 mc at 30 mc and using an 18 mc offset frequency, there may appear as many as seven spurious frequencies, each corresponding to a different harmonic combination of signals in the canceller mixers. While the levels of these spurious signals are relatively low and usually tolerable in systems of this bandwidth, any increase in bandwidth as desired in many applications may result in unacceptably high spurious signal levels.